A Study to Investigate the Safety, Tolerability, Pharmacokinetics, Pharmacodynamics and Efficacy of Risdiplam (RO7034067) in Type 2 and 3 Spinal Muscular Atrophy (SMA) Participants

Inclusion Criteria:

* Confirmed diagnosis of 5q-autosomal recessive SMA
* Negative blood pregnancy test at screening and agreement to comply with measures to prevent pregnancy and restrictions on sperm donation
* For Part 1: Type 2 or 3 SMA ambulant or non-ambulant
* For Part 2: 1) Type 2 or 3 SMA non-ambulant; 2) RULM entry item A greater than or equal to 2; 3) ability to sit independently as assessed by item 9 of the MFM

Exclusion Criteria:

* Concomitant or previous participation in any investigational drug or device study within 90 days prior to screening, or 5 half-lives of the drug, whichever is longer
* Concomitant or previous administration of a SMN2-targeting antisense oligonucleotide, SMN2 splicing modifier or gene therapy either in a clinical study or as part of medical care
* Any history of cell therapy
* Hospitalization for a pulmonary event within the last 2 months or planned at time of screening
* Surgery for scoliosis or hip fixation in the one year preceding screening or planned within the next 18 months
* Unstable gastrointestinal, renal, hepatic, endocrine, or cardiovascular system diseases as considered to be clinically significant by the Investigator
* Presence of clinically significant electrocardiogram abnormalities before study drug administration from average of triplicate measurement or cardiovascular disease indicating a safety risk for participants as determined by the Investigator
* Any major illness within one month before the screening examination or any febrile illness within one week prior to screening and up to first dose administration
* Recently initiated treatment (within less than \[\<\] 6 months prior to randomization) with oral salbutamol or another beta 2-adrenergic agonist taken orally
* Any prior use of chloroquine, hydroxychloroquine, retigabin, vigabatrin or thioridazine, is not allowed
* Ascertained or presumptive hypersensitivity (e.g., anaphylactic reaction) to Risdiplam or to the constituents of its formulation
* Recent history (less than one year) of ophthalmological diseases
* Participants requiring invasive ventilation or tracheostomy